Radio-Frequency Identification (RFID) systems typically include RFID readers, also known as RFID reader/writers or RFID interrogators, and RFID tags. RFID systems can be used to inventory, locate, identify, authenticate, configure, enable/disable, and monitor items to which the tags are attached or in which the tags are embedded. RFID systems may be used in retail applications to inventory and track items; in consumer- and industrial-electronics applications to configure and monitor items; in security applications to prevent loss or theft of items; in anti-counterfeiting applications to ensure item authenticity; and in myriad other applications.
RFID systems operate by an RFID reader interrogating one or more tags using a Radio Frequency (RF) wave. The RF wave is typically electromagnetic, at least in the far field. The RF wave can also be predominantly electric or magnetic in the near field. The RF wave may encode one or more commands that instruct the tags to perform one or more actions.
A tag that senses the interrogating RF wave may respond by transmitting back a responding RF wave (a response). A tag may generate the response either originally, or by reflecting back a portion of the interrogating RF wave in a process known as backscatter. Backscatter may take place in a number of ways.
The reader receives, demodulates, and decodes the response. The decoded response may include data stored in the tag such as a serial number, price, date, time, destination, encrypted message, electronic signature, other data, any combination of tag data, and so on. The decoded response may also include status information or attributes about the tag or item such as a tag status message, item status message, configuration data, and so on.
An RFID tag typically includes an antenna and an RFID integrated circuit (IC) comprising a radio section, a power management section, and frequently a logical section, a memory, or both. In some RFID ICs, the logical section may include a cryptographic algorithm which may rely on one or more passwords or keys stored in tag memory. In earlier RFID tags the power management section often used an energy storage device such as a battery. RFID tags with an energy storage device are known as battery-assisted, semi-active, or active tags. Advances in semiconductor technology have miniaturized the IC electronics so much that an RFID tag can be powered solely by the RF signal it receives. Such RFID tags do not include an energy storage device and are called passive tags. Of course, even passive tags typically include temporary energy- and data/flag-storage elements such as capacitors or inductors.
In typical RFID tags the IC is electrically coupled to the antenna, which in turn is disposed on a substrate. As technology advances and ICs shrink, assembling, aligning, and coupling the IC to the antenna becomes challenging.